The present invention is generally directed to implantable medical devices and in particular battery-powered implantable medical devices and systems for communicating with such devices.
The present invention relates to systems for monitoring and/or affecting parameters of a patient""s body for the purpose of medical diagnosis and/or treatment. More particularly, systems in accordance with the invention are characterized by a plurality of devices, preferably battery powered, configured for implanting within a patient""s body, each device being configured to sense a body parameter, e.g., temperature, O2 content, physical position, electrical potential, etc., and/or to affect a parameter, e.g., via nerve and/or muscle stimulation.
Commonly owned U.S. Pat. No. 6,164,284 entitled xe2x80x9cSystem of Implantable Devices For Monitoring and/or Affecting Body Parametersxe2x80x9d and U.S. Pat. No. 6,185,452 entitled xe2x80x9cBattery Powered Patient Implantable Devicexe2x80x9d, incorporated herein by reference in their entirety, describe devices configured for implantation within a patient""s body, i.e., beneath a patient""s skin, for performing various functions including: (1) stimulation of body tissue and/or sensing of body parameters, and (2) communicating between implanted devices and devices external to a patient""s body. Depending upon the ailment affecting the patient, it may be desirable to communicate with a number of different devices, e.g., from one to thousands, while maintaining an update rate, e.g., on the order of every 1 millisecond to every second, sufficient to control and/or monitor the body parameter(s) at issue. Such implantable devices are preferably powered using rechargeable batteries. Depending on the power requirements of these devices and the available capacity of their rechargeable batteries, the time between rechargings is potentially limited. Accordingly, power conservation techniques to extend the battery life of such devices are desirable. The present invention is directed to a multichannel communication system and protocol that facilitate such power conservation while maintaining the required update rate.
The present invention is directed to a communication system and protocol that is configured to extend the battery life of battery-powered devices that monitor and/or affect parameters of a patient""s body and is particularly useful in a system comprised of a system control unit (SCU) and one or more devices implanted in the patient""s body, i.e., within the envelope defined by the patient""s skin. Each such implanted device is configured to be monitored and/or controlled by the SCU via a wireless communication channel.
In accordance with the invention, the SCU comprises a programmable unit capable of (1) transmitting commands to at least some of a plurality of implanted devices and (2) receiving data signals from at least some of those implanted devices. In accordance with a preferred embodiment, the system operates in closed loop fashion whereby the commands transmitted by the SCU are dependent, in part, on the content of the data signals received by the SCU.
In accordance with an exemplary embodiment, each implanted device is configured similarly to the devices described in the commonly owned U.S. Pat. No. 6,164,284 and typically comprises a sealed housing suitable for injection into the patient""s body. Each housing preferably contains a power source having a capacity of at least 1 microwatt-hour and power consuming circuitry preferably including a data signal transmitter and receiver and sensor/stimulator circuitry for driving an input/output transducer. Wireless communication between the SCU and the other implanted devices can be implemented in various ways, e.g., via a modulated sound signal, an AC magnetic field, an RF signal, a propagated electromagnetic wave, a light signal, or electrical conduction.
Preferably such implantable devices are powered by an internal rechargeable battery. The amount of time between rechargings of the battery is determined by the battery capacity and the power consumption of the device. The present invention reduces the average power consumption of the implantable devices by reducing the usage duty cycle of the power consuming transmit and receive modes used by the implantable devices to communicate with the SCU while maintaining a sufficient update rate to control and/or monitor the required body parameter(s). By dedicating addressable time slots to each of the implantable devices in the system and limiting their use of receive and transmit modes to time periods proximate to these time slots, the average power consumption is accordingly reduced.
In accordance with the present invention, a preferred method is described for communicating between a system controller and a plurality of addressable, battery-powered, implantable stimulation/sensor devices that is configured to extend the battery life of the implantable devices by reducing their average power consumption. In the preferred method, the system controller periodically, during a system control data time period, sends a system control data message which defines addressable data that is to be directed to each of the plurality of implantable devices, wherein the implantable devices consume a base amount of power and additionally consume a first incremental amount of power when operating in a receive mode to receive data from the system controller during a selected portion of the system control data time period, the selected portion of the system control data time period being a portion, i.e., less than 75%, of the system control data time period and the average power consumption of the implantable devices is reduced accordingly. The system controller then waits a response time period following each system control data message for enabling each of the implantable devices to provide data to the system controller in a selected portion of the response time period related to the address of each implantable device, wherein the implantable devices additionally consume a second incremental amount of power when operating in the transmit mode, the selected portion of the response time period being a portion, i.e., less than 75%, of the response time period and the average power consumption of the implantable devices is reduced accordingly.
In accordance with a further aspect of the invention, the implantable devices are configurable to switch between a first mode of operation where the selected portion of the response time period is used for responses from a single implantable device and a second mode of operation where the selected portion of the response time period is alternately shared for sending responses to the system controller from a plurality of implantable devices, thereby extending the battery life of the implantable devices that share the selected time response period portions.
In a still further aspect of the present invention at least one selected implantable device is configurable via data within the system control data message to occupy a plurality of the selected portions of the response time period to thereby increase the effective communication rate from the selected implantable device to the system controller.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
FIG. 1 is a simplified block diagram of an exemplary system suitable for practicing the communication protocol of the present invention, the system being comprised of implanted devices, e.g., microstimulators, microsensors and microtransponders, under control of an implanted system control unit (SCU).
FIG. 2 comprises a block diagram of the system of FIG. 1 showing the functional elements that form the system control unit and implanted microstimulators, microsensors and microtransponders.
FIG. 3A comprises a block diagram of an exemplary implantable device, as shown in U.S. Pat. No. 6,164,284, including a battery for powering the device for a period of time in excess of one hour in response to a command from the system control unit.
FIG. 3B comprises a simplified block diagram of controller circuitry that can be substituted for the controller circuitry of FIG. 3A, thus permitting a single device to be configured as a system control unit and/or a microstimulator and/or a microsensor and/or a microtransponder.
FIG. 4 shows an exemplary flow chart of the use of the exemplary system in an open loop mode for controlling/monitoring a plurality of implanted devices, e.g., microstimulators, microsensors.
FIG. 5 shows a simplified flow chart of the use of closed loop control of a microstimulator by altering commands from the system control unit in response to status data received from a microsensor.
FIG. 6 shows an exemplary injury, i.e., a damaged nerve, and the placement of a plurality of implanted devices, i.e., microstimulators, microsensors and a microtransponder under control of the system control unit for xe2x80x9creplacingxe2x80x9d the damaged nerve.
FIG. 7 shows a simplified flow chart of the control of the implanted devices of FIG. 6 by the system control unit.
FIG. 8 shows a side cutaway view of an exemplary implantable ceramic tube suitable for the housing the system control unit and/or microstimulators and/or microsensors and/or microtransponders.
FIG. 9 is a simplified diagram of a communication protocol configured to extend the battery life of an implantable device.
FIG. 10 is a simplified block diagram of an implantable device, such as that shown in FIG. 3A, that is particularly directed to the power consumption features facilitated by the communication protocol of FIG. 9.
FIG. 11 shows a simplified diagram of multiple systems using the communication protocol of the present invention by intertwining their use of the available communication channel.
FIGS. 12A and 12B show simplified diagrams of the effects of changing the number of time slots associated with the SCU and the implantable devices.
FIG. 13 shows a simplified diagram of the interrogation between a plurality of systems, i.e., SCUs and implantable devices, to allow the systems to coexist in a restricted location.
FIGS. 14A and 14B show exemplary implementations of antennas that may be used with embodiments of the present invention.